Malignant melanoma. Light micrograph (LM) of a section through human skin showing melanoma cancer (brown bottom of image). The skin epithelium is at the top of the image.This cancer arises from the skin's melanocytes, the cells that produce the pigment (melanin) that give skin its colour.The main cause of melanoma is exposure to ultraviolet radiation in sunlight. It is an aggressive cancer that often spreads (metastasises) to other tissues of the body. Treatment is with surgical removal of the tumour, often combined with chemotherapy and/or immunotherapy. However, once the cancer has spread, the prognosis is poor. Magnification: x 25 when printed 10cm wide.